In the related art, a barium titanate ceramics which is a lead-free piezoelectric ceramics is obtained by crashing and mixing barium carbonate (BaCO3) and titanium oxide (TiO2) and sintering for 4 hours under a temperature of 1300 degrees to 1400 degrees. However, in the barium titanate ceramics obtained in this manner, the Curie temperature which is a temperature in which the piezoelectric characteristic is lost is relatively low and a piezoelectric constant d33 is lower than 200 pm/V, and, thus, the ceramics is not practical.
In recent years, a composition of and a method of manufacturing a niobate-based (KNbO3—NaNbO3—LiNbO3-based) ceramics having a relatively high piezoelectric characteristic have been found (Non-patent Document 1), and a structure has been obtained which is close to practical such as a Curie temperature of about 250° C. and a piezoelectric constant d33 of about 400 pm/V.
In addition, an example is known in which a barium titanate (BaTiO3) powder of a nano-size material which is hydrothermally synthesized is sintered in a range of 1050° C. to 1200° C. to achieve a piezoelectric constant d33 which is close to 400 pm/V (Patent Document 1).
Moreover, an experimental example is known in which two stages of sintering is applied and a barium titanate ceramics is obtained in which the performance is improved (Non-patent Document 2).